Adhesives are used frequently in the fabrication of electronic devices, for example, to attach individual semiconductor dies to substrates. In one method of semiconductor assembly, a semiconductor die is adhered to its substrate with a paste or film adhesive. The assembly is then subjected to heat to cure the adhesive so that it develops sufficient strength to survive subsequent processing steps and to eliminate voids formed by out-gassing during these later fabrication stages. Depending on the adhesive chemistry, this cure schedule can be as long as an hour. The active terminals on the surface of the semiconductor die are then connected to the active terminals on the substrate with metal wires in an automated operation known as wire bonding, which occurs at about 125° to 210° C. After wire bonding, the assembly is encapsulated in a molding compound to protect the active surface of the semiconductor and the wire bonds. This molding operation occurs at about 170° to 180° C. The need for the heat treatment to cure the die attach adhesive before the wire bonding and molding operations reduces manufacturing throughput significantly and is especially inefficient when the fabrication requires multi-die stacking.
The current trend in semiconductor packaging fabrication favors completing as many process steps as possible at the silicon wafer level, before the wafer is diced into individual semiconductor dies. A further trend for stacked die packages is to combine or eliminate as many cure steps as possible. This allows multiple semiconductor dies to be processed at the same time, making the fabrication process more efficient. One step that can occur at the wafer level is the application of the adhesive for attaching the semiconductor dies to substrates. The adhesive is commonly known as a wafer backside coating adhesive and is typically applied by screen or stencil printing, spin-coating, or nozzle spraying. After application, the coating is thermally or photochemically treated to evaporate solvent and/or partially advance the adhesive resin (known as B-staging). This strengthens the adhesive for the further fabrication processes.
Thus, it would be an advantage to provide an adhesive that has sufficient adhesive strength to withstand the subsequent processing steps without needing an extra cure stage after die attach.